1. Field of the Invention
The invention relates to compositions comprising antimony dithiocarbamates in combination with ammonium or zinc dithiocarbamates, as additives for lubricating grease in order to provide extreme pressure (EP) protection while reducing the amount of antimony. The addition of a compound containing at least one carboxylic acid functional group can act to avoid or reduce the copper corrosion effect resulting from the use of antimony, and antimony in combination with ammonium dithiocarbamate.
2. Description of the Prior Art
Antimony dithiocarbamates are well known in the art for their usefulness as extreme pressure (EP) agents, and are exceptionally useful as EP additives in lubricating greases. Representative patents disclosing the use of antimony dithiocarbamates are U.S. Pat. Nos. 3,139,405 and 5,246,604, which are incorporated herein by reference. However, environmental and health issues are restricting antimony levels in lubricants and greases.
Accordingly, there is a need for compositions which boost EP performance of antimony dithiocarbamates in soap-based greases, allowing for a reduction in the effective amount of antimony needed to maintain desired performance.
Specifically, the EP performance is improved by preparing antimony dithiocarbamate compositions containing ammonium dithiocarbamate and/or zinc dithiocarbamate. Antimony dithiocarbamates and antimony dithiocarbamate compositions described above can be corrosive to nonferrous metals such as copper when used in soap-based greases. The present invention teaches that compounds containing carboxylic acid functional groups are effective copper corrosion inhibitors for these grease compositions.